When a measurement target object is irradiated with illumination light, light reflected by the surface of the measurement target object sometimes contains scattered light. The scattered light scatters not in the regular reflection direction with respect to the incident angle of light but in various directions. The scattered light is generated by a microstructure of 760 nm or less formed on the surface of the measurement target object.
A BRDF apparatus measures scattered light. “BRDF” is a short for “Bi-directional Reflectance Distribution Function”.
The BRDF is a function that returns the reflection angle of light using the incident angle or wavelength of light as an argument, and changes depending on the material or microstructure of a predetermined substance. The BRDF is mainly used to express the surface state or texture of a predetermined substance in virtual space.
Patent reference 1 discloses a BRDF measurement apparatus that supports multibands containing four or more color components.    [Patent Reference 1] Japanese Patent Laid-Open No. 2006-275955
A demand has recently grown for measuring not only the surface shape of a measurement target but also the microstructure formed on the surface of the measurement target. The conventional BRDF apparatus can measure the BRDF on the surface of a measurement target object but does not propose to measure the surface shape of a measurement target.